1. Field of the Invention
The present invention relates to an image adjustment processing in an image forming apparatus, and, more particularly to improvement of accuracy of image adjustment processing.
2. Description of the Related Art
In recent years, color MFPs are becoming increasingly popular year by year. In particular, since office documents are prepared in color, an increasing number of color copies and prints are used. In the case of the color MFPs, it is more important to always keep colors and densities constant. However, in general, a density characteristic of a printer engine tends to change as time elapses. Thus, some the color MFPs have a function for gamma automatic adjustment (calibration) to keep colors and gradations as constant as possible.
Specifically, the gamma automatic adjustment is a function of outputting, in general, a pattern of a regular gradation, inputting the pattern with a scanner, calculating an inverse function or the like from a read value, and setting a gamma correction curve for adjusting an output image quality.
A gray section other than characters of a copy and a print image is often formed by four colors of Y/M/C/K. However, in this gray section, since a balance of the respective colors is lost because of aged deterioration and a difference among machines, the gray changes to colored gray, which looks extremely unattractive. When the gray balance is lost in this way, conventionally, it is possible to adjust the gray balance using a function of color balance adjustment or the like. However, this takes time because the adjustment is manual adjustment. Further, even if the gray balance is adjusted with effort, a printer gamma characteristic (an image formation characteristic) fluctuates due to aged deterioration. Thus, the gray balance has to be adjusted every time the printer gamma characteristic fluctuates, which is extremely complicated.
Moreover, even if the gray balance is successfully corrected in this way, when unexpected density unevenness of a toner image occurs on an identical sheet, it is extremely difficult to perform image adjustment. There is a problem in that it is impossible to accurately correct the gray balance even if automatic adjustment is performed in this state.